Use the same function to join the root paths for the wrapping remotes
alias, cache and crypt.
The new function fspath.JoinRootPath is equivalent to path.Join, but if
the first non empty element starts with "//", this is preserved to allow
Windows network path to be used in these remotes.
This change allows remotes to be created on the fly without a config
file by using the remote type prefixed with a : as the remote name, Eg
:s3: to make an s3 remote.
This assumes the user is supplying the backend config via command line
flags or environment variables.
Before this copyto would parse windows paths incorrectly.
This change moves the parsing code into fspath and makes sure
fspath.Split calls fspath.Parse which does the parsing correctly for
This also renames fspath.RemoteParse to fspath.Parse for consistency
The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.
The new code layout is documented in CONTRIBUTING.
